One of the misconceptions that circulate on this site is the idea that a journaled HFS volume can be corrupted by a forced unmount, as for example in a system crash or a power failure. This is false. With filesystem journaling, when the volume is remounted after a forced unmount, the directory is automatically repaired, and files are restored to their previous state, using redundant information (the journal) stored on the drive. This is very well established technology, and for all practical purposes, it always works, unless the journal itself is corrupt due to a hardware failure in the drive. So if the directory of a journaled volume is found to be corrupt, the storage device hosting the volume has thrown at least one unrecoverable hardware error.
People who don't understand journaling will tell you to repair the corrupt volume with Disk Utility (if possible), or with Disk Warrior otherwise, and then go on using the drive as if everything is fine. That might have been good advice years ago, before the introduction of HFS journaling, when it was common for volumes to be corrupted as the result of forced unmounting. Today, because forced unmounts no longer cause that kind of corruption, it's relatively rare – or should be – and when it does happen, the implications are different.
My opinion is that when a drive throws such a severe error that a volume directory not only can't be restored by journal replay, but also can't be repaired by Disk Utility, that drive should no longer be trusted with data. It should be taken to a recycling center.
But even if you do choose to go on trusting the drive, if you have backups, you shouldn’t try to scavenge the directory with Disk Warrior. You should erase the volume and restore the data from your backups. Doing that is faster, safer, and cheaper than using DW. DW should be reserved for those situations where there are no backups, and even then, the drive should still be erased, or preferably retired, after the data is recovered.
Deric Horn, the head of filesystem engineering at Apple, gave a presentation at WWDC 2012 in which he stated, with regard to journaled HFS (starting at offset 3:18 in the recording) "The journal means that you can pull power at any time, and your filesystem is still intact. The shouldn't be any data corruption or any volume corruption on that disk." You can hear that presentation by registering for a free developer account and going to this page:
WWDC 2012 Session Videos - Apple Developer
Look for "What's New In The Filesystem" near the bottom of the page.
If a poster on this site knows more about HFS than the Apple developer in charge of it, then Horn should be fired, and the ASC poster should get his job. Until that happens, I suggest you believe what Horn says.
